The present invention is directed to apparatus for moving an entire video display in a scrolling fashion and more particularly to a video game in which the display is scrolled in the horizontal direction under synchronous microprocessor control in response to player inputs.
In a video system where it is desired to display selected video portions of a larger available field, one technique has been to use a mechanical pictorial map with the television camera on an XY table; that is, a table which moves left and right or up and down. Such a technique is termed "scrolling" since the field is effectively being scrolled past the video camera from a relative motion standpoint. An analogous non-mechanical known technique uses a large capacity graphics computer which has the entire field stored in a pictorial memory, the computer providing a window on that memory to produce the display world on the TV screen. This latter method, of course, requires a very large program memory.
One technique for scrolling in the vertical direction only is shown in commonly assigned, co-pending Application Ser. No. 868,932, filed Jan. 12, 1978, now U.S. Pat. No. 4,169,272, issued Sept. 25, 1979, entitled "Apparatus for Simulating a Perspective View of a Video Image and for Storing Such Image With a Minimum Number of Bits" in the name of Rains, et al. This technique utilizes a vertical counter to directly address a graphics read-only memory (ROM) at different locations. Such a ROM, of course, includes the entire field. The technique, however, is not particularly adaptable to scrolling in a horizontal direction.
It can be seen, therefore, that there exists a need for apparatus capable of scrolling a video display in a horizontal direction, which utilizes a minimum of memory space and circuitry. Such a technique would obviate the need for expensive and complex apparatus such as television cameras or large program memories described above.